The present invention relates to a filter rod measuring station as well as a method for measuring the mass of a softener, the moisture and/or the dry filter material in a filter rod as used as a cigarette filter.
During the manufacture of cigarette filters, in a filter rod machine a plug is formed from a cellulose acetate filter tow. The plug is sprayed with a softener, the fibres of the filter material welded to one another and thus a dimensional stability is created for the filter rod. The softener, generally triacetin, provides the desired filter effect by the cross-linking of the fibres and ensures that even during a subsequent smoking process, the filter remains in shape. This is especially important as, during the smoking process, a not inconsiderable amount of water vapour also flows through the filter.
The filter effect of a cellulose acetate filter depends on the type of fibre material of the filter tow used. The fibre material of the filter tow is identified by the provision of its titre.
In addition to being dependent on the material, the filter effect also depends on the total density of the filter tow used and the type of cross-linking of the fibres. The cross-linking of the fibres is quite substantially determined by the amount of triacetin used. During the manufacture of cigarette filters it is generally desired to achieve a filter effect which is as high as possible for the tobacco smoke condensate with as little draw resistance as possible. The draw resistance is the pressure loss via a filter with constant air flow.
A method and a device for measuring the triacetin content in filter plugs, during the production thereof, is known from EP 1 197 746 A1. A microwave measuring device is used in the method which, before and after the addition of triacetin, detects two measured variables determining the mass and the moisture. The mass of the added triacetin may be determined from the measured variables obtained. The method is used in the production process line, before and after the addition of triacetin.
The simultaneous acetate and triacetin measurement according to WO 03/070030 A1 is also carried out in a machine for manufacturing cigarette filters. A measurement of the mass flow of filter tow material through the machine is carried out, as well as a measurement of the mass of softener used. In this connection a microwave measuring device is used. A measurement is also carried out with this attachment during the manufacturing process, whereby it is necessary to install two sensors in the machine, once before the addition of the softener and once after the addition of the softener.
These online methods are, however, only usable where the required space for the installation of a microwave sensor is also available on the filter plug in the filter rod machine. Moreover, with the one sensor plug method, even here the problem of the occasional production of rejects occurs by periodically disconnecting the triacetin for determining the mass of the filter rod without triacetin.